Diamond research activities have increased dramatically in recent years, an outcome fueled primarily by diamonds' superior mechanical, thermal, and optical properties. It is known to have the highest thermal conductivity while being an excellent electrical insulator. Furthermore, it is an extremely hard material, has excellent corrosion resistance, and transmits optically over a broad wavelength range..sup.1,2 These properties lead to many potential applications for diamond coatings as well as free standing films..sup.3 Research in the chemical vapor deposition (CVD) of diamond has led to the development and use of many different synthesis techniques, ranging from hot filament and microwave activation.sup.1,2 (generally at low pressures) to arc.sup.4,5 and flame.sup.6,7 excitation (generally near atmospheric pressure). High quality diamond in thin film form to free standing samples of several millimeter thickness are now commercially available.
Despite the progress that has been observed in the manufacture of engineered diamond, little is known about the chemistry controlling nucleation and growth. Identification of the growth precursors and mechanisms for carbon incorporation into the growing diamond surface is now the subject of intense experimental and theoretical research. Detailed mechanisms based on both methyl .sup.8,9 (CH.sub.3) and actylene .sup.10 (C.sub.2 H.sub.2) as precursors have been proposed recently. As most synthesis strategies rely on the production of copious amounts of atomic hydrogen, it is now generally believed that atomic hydrogen plays an important role in growth kinetics by preventing surface reconstruction of the growing diamond film (i.e. stabilizing sp.sup.3 hybridized surface carbon bonds), and by producing active sites through abstraction of surface hydrogen..sup.2,11 These active sites are now available to react with possible growth precursors.
DC arcjets have proven to be of great potential in diamond synthesis,.sup.12-18 for they deliver the highest linear growth rates at nearly 1 mm per hour while still retaining excellent quality..sup.12